High-pressure phase diagram of an aluminium-rich Al-Li alloy at a pressure of 5.4 GPa

The high-pressure phase diagram of an aluminium-rich Al-Li alloy at a 5.4 GPa pressure was investigated. To determine the equilibrium state under high-pressure and high-temperature conditions, the quenching method was applied and a phase analysis of the sample was performed using X-ray diffraction and microscopic observations. The experimental results were then compared with a thermodynamic theoretical calculation and good agreement was found. The resultant solid solubility of lithium in aluminium was subsequently increased up to 20 at % and the eutectic temperature increased up to 800 °C.     

Isobaric sections of the aluminium phase field in the Al-Ge phase diagram at high pressures up to 2.6 GPa

The isobaric sections of the aluminium phase field in the Al-Ge system have been obtained experimentally at 0.1 MPa, 2.2 and 2.6 GPa. The solidus and solid solubility lines of the aluminium phase were determined by electron probe microanalysis of alloys quenched after equilibration at known temperatures and pressures. The aluminium phase field of aluminium was observed to expand with increasing pressure. This result was compared with the phase diagrams calculated on the basis of thermodynamic and volumetric data at 0.1 MPa. The calculations are in qualitative agreement with the experimental results.     

Electrical resistance of platinum at a pressure of up to 1 GPa

The effect of a high hydrostatic pressure of up to 1 GPa on the electrical resistance of platinum in the 20–100°C temperature range is investigated. An approximate formula is proposed for correcting the readings of platinum resistance thermometers used in a medium under high hydrostatic pressures.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 39–40, February, 1994.     

Phase diagram of the Mg-O system at a pressure of 2 GPa

Thermodynamic calculation and experimental studies of the phase quilibria in the Mg-O system have been performed and the system phase diagram at a pressure of 2 GPa has been constructed. The system is characterized by the existence of just one eutectic equilibrium at 1100 K, in which magnesium, MgO magnesium oxide, and a liquid phase take part.     

Shock adiabat of a one-velocity heterogeneous medium

An expression for the shock adiabat of a multicomponent mixture has been obtained. It agrees with the equations of the one-velocity model of a heterogeneous medium. The predictions are compared with the generally used shock adiabat equation based on the assumption on additive shock compression of mixture components. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 46–52, September–October, 2006.     

Thermodynamic calculation of the melting diagram of the Mg-MgO-B system at a pressure of 2 GPa

Phase equilibria with the participation of a liquid phase in the Mg-MgO-B ternary system at 2 GPa have been calculated in the framework of model approximations of the phenomenological thermodynamics. The melting diagram of the system is characterized by five nonvariant four-phase equilibria, three of which are peritectic and two eutectic ones. The region of the primary crystallization of magnesium diboride MgB₂ in the diagram is near the Mg-B binary system region and as the oxygen concentration increases, disappears and is replaced by the crystallization regions of MgO and MgB₄ at the point of peritectic equilibrium L + MgB₂ ? MgO + MgB₄ (1345 K, 68 at % B, 10 at % O).     

Measurements of the viscosity of benzene,toluene, and m-xylene at pressure up to 80 MPa

New absolute measurements of the viscosity of benzene, toluene, and m-xylene are presented. The measurements were performed in a recently developed vibrating-wire instrument, at temperatures of 303.15 and 323.15 K and pressures up to 80 MPa. The overall uncertainty in the reported viscosity data is estimated to be ±0.5%.     

Equation-of-state measurements for crude oils at pressures up to 1 GPa

Equation-of-state measurements of two crude oils with different compositions and viscosity were performed at room temperature in the pressure range 0<P<1.0 GPa. We found large compressibilities and a strong dependence of the compressibility on oil content and viscosity. The bulk modulus changed with pressure from 2.0 to 12.1 GPa for one oil and from 1.3 to 9.5 GPa for the other. We discuss the possibility of detecting phase transitions in the region under investigation. The Tait and Murnaghan equations of state were fitted to the data, and residuals are presented.     

Modeling of Liquid Silicon at Pressures up to 23 GPa from Diffraction Data

Earlier reported diffraction data for silicon at pressures of 4, 8, 14, and 23 GPa and temperatures 50 K above the melting point are used to develop models of liquid silicon (2997 particles in a cubic central box with periodic boundary conditions) and reconstruct the effective pair potential, which is found to depend little on density and temperature. It is shown that, between 8 and 14 GPa, the structure of liquid silicon becomes markedly denser. The calculated self-diffusion coefficient of liquid silicon decreases almost twofold with increasing pressure.     

Resistivity and Hall Coefficient of Zinc Diarsenide at Hydrostatic Pressures of up to 9 GPa

The electrical properties of ZnAs₂ single crystals were measured along the [001] direction in the pressure range from 0 to 9 GPa. The electrical resistivity of the crystals was found to decrease by one order of magnitude as the pressure increases from 0 to 7 GPa, without significant changes at higher pressures. The Hall coefficient drops by two orders of magnitude as the pressure increases from 0 to 7 GPa and remains constant in the range from 7 to 9 GPa.     

Measurements of the viscosity of n-heptane,n-nonane,and n-undecane at pressures up to 70 MPa

New absolute measurements of the viscosity of n-heptane, n-nonane, and n-undecane are presented. The measurements were performed with a vibrating-wire instrument at temperatures of 303.15 and 323.15 K and pressures up to 70 MPa. The overall uncertainty in the reported viscosity data is estimated to be ±0.5%. A recently developed semiempirical scheme for the correlation and prediction of the thermal conductivity, viscosity, and self-diffusion coefficients of n-alkanes is applied to the prediction of the viscosity of n-heptane, n-nonane, and n-undecane. The comparison of these predicted values with the present high-pressure measurements demonstrates the predictive power of this scheme.     

The viscosity of liquid water at pressures up to 32 MPa

The paper reports new, preliminary measurements of the viscosity of liquid water along two isotherms as a function of pressure up to 32 MPa. The measurements have been performed with a vibrating-wire viscometer especially modified for the purpose. The instrument has been calibrated with respect to the viscosity of water at a pressure of 0.1 MPa and a temperature of 293.15 K, for which an accurate reference value is available. With due regard to the precision of the determination of individual quantities and the accuracy of the calibration data, it is estimated that the accuracy of the present results is one of ±0.3% under all conditions.Paper dedicated to Professor Joseph Kestin.     

Elastic moduli of Al-Li alloys treated at a high pressure of 5.4 GPa

The elastic moduli of high pressure treated supersaturated Al-Li solid solutions were measured. An interesting elastic behaviour was observed, in that, the bulk modulus decreased with an increase in the lithium content, whereas the Young's modulus and shear modulus increased. In order to clarify this property, we investigated the compressibility of the Al-Li supersaturated solid solutions prepared by high-pressure solid-solidification by high-pressure Synchrotron X-ray diffraction. The obtained pressure-volume relations were fitted to Birch's equation of state. The calculated bulk moduli were lower than those of pure Al at a reduction of about 0.6 GPa per mol% Li. The temperature dependence of the elastic modulus for those supersaturated solid solutions was also measured, and it was found that the trend in the variation of the elastic modulus against the lithium concentration was maintained in the temperature range of 5–290 K. Therefore the attractive relationship between the bulk modulus and Young's modulus was demonstrated to be intrinsic.     

The pressure-volume relation of ytterbium up to 9 GPa

The pressure-volume relation of ytterbium has been determined up to 9 Gpa using tungsten carbide opposed anvil high pressure x-ray camera. The fcc phase of ytterbium is observed between one atmosphere and 4 GPa and the bcc phase above 3·5 GPa. The bcc phase can be metastably retained down to 1 GPa by gradually decreasing the pressure from a region where only bcc phase alone is observed. The bulk modulus,B ₀, at zero pressure and the pressure derivative of the bulk modulus,B’ ₀, are determined by fitting Murnaghan equation to the pressure-volume data. The following values were obtained:B ₀=16·3 GPa andB’ ₀=3·6 for the fcc phase, andB ₀=14·7 GPa andB’ ₀=1·5 for the bcc phase. Based on the present data it is suggested that the thermodynamic equilibrium pressure for fcc ⇆ bcc transformation in ytterbium is below 3·5 GPa. The valence change under pressure has been discussed.     

The viscosity of five liquid hydrocarbons at pressures up to 250 MPa

This paper reports new measurements of the viscosity of toluene, n-pentane, n-hexane, n-octane, and n-decane at pressures up to 250 MPa in the temperature range 303 to 348 K. The measurements were performed with a vibrating-wire viscometer and with a relative method of evaluation. Calibration of the instrument was carried out with respect to reference values of the viscosity of the same liquids at their saturation vapour pressure. The viscosity measurements have a precision of ±0.1% but the accuracy is limited by that of the calibration data to be ±0.5%. The experimental data have been represented by polynomial functions of pressure for the purposes of interpolation. The data are also used as the most precise test yet applied to a representation of the viscosity of liquids based upon hard-sphere theory.     

Thermoelectric power of YBa2Cu3O7−δ under pressure up to 9 GPa

Thermoelectric power (TEP) of two YBa₂Cu₃O_7−δ compounds (with δ=0·17 and 0·21) was measured as a function of quasi-hydrostatic pressure up to 9GPa at 300K on samples with low porosity. In both cases TEP decreases with increasing pressure, at a rate ∼ 0·8 μVK⁻¹/GPa. The data obtained under hydrostatic pressure up to 3 GPa are in good agreement with those under quasi-hydrostatic pressure. The TEP of both compositions is found to decrease linearly at a rate 0·8 μVK⁻¹/GPa above 1·5 GPa.     

Superconducting and mechanical properties of YBCO/Ag composites fabricated at high pressures up to 5.4 GPa

The YBCO/Ag superconducting composites were fabricated by compressing powders of YBCO and silver mixed at various volume proportions 0 to 100% under pressures of 2.0 and 5.4 GPa and subsequently sintering at 900 °C for 10 h in a flowing oxygen atmosphere. The superconducting transition temperature, particularlyT _c (R=0), was found to retain the value above 85 K up to 50 vol % Ag while the normal resistivity at 300 K to reduce below 10 cm. The highestJ _c of 400 Acm^–2 was attained for the sample containing 20 vol % Ag pressed at 5.4 GPa. The mechanical properties were also improved by the addition of silver: the compressive strength is increased by two to three times and the maximum strain, which is a measure of ductility, reached a value almost four times as large as that in the pure YBCO prepared under the ordinary pressure of 0.5 GPa. The persistence of the superconducting characteristics up to 70 vol % Ag is discussed in terms of the microstructure taken with the scanning electron microscope.